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Force Mass and Motion Unit - Day 3
Tuesday, December 03, 2013
2:26 PM
SPS8. Determine relationships among force, mass, and motion.
c. Relate falling objects to gravitational force
d. Explain the difference in mass and weight.
Assessment: Mini-quest over c and d at the end of class.
Define:
Gravity - ?????? - attractive force between 2 bodies depends on the masses and their distance
Force (again) - push or pull on an object
Mass (again) - amount of matter in an object
Weight - gravitational force on an object
What goes up must come down - WHY? gravity
What pulls objects downwards? gravity
Gravity Demos. g = -9.8 m/s2
Projectile Motion (Demo) - curved downward motion (arc) due to gravity and horizontal
velocity
Weight: Fg = mg
Weight Probs:
4. Find the weight of a 60 kg astronaut on earth
a. Find the weight of the same object on a planet where the gravitational attraction
has been reduced to 1/10 of the earth’s pull. Show all work.
5. A backpack weighs 8.2 newtons and has a mass of 5 kg on the moon. What is the
strength of gravity on the moon? (Be careful with units, remember 1N= 1 kg  m/s2)
Fg = mg
8.2 = 5g
g= 8.2 / 5 = 1.64 m/s2
6. A physical science test book has a mass of 2.2 kg
Physical Science Page 1
6. A physical science test book has a mass of 2.2 kg
a. What is the weight on the Earth? Fg = 2.2 x 9.8 = 21.56
b. What is the weight on Mars (g = 3.7 m/s2 ) Fg = mg = 2.2 x 3.7 = 8.1400
c. If the textbook weights 19.6 newtons on Venus, What is the strength of gravity
on Venus? Fg = mg; 19.6 = 2.2g; g = 19.6 / 2.2 = 8.9091
7. Of all the planets in our solar system, Jupiter has the greatest gravitational strength.
a. If a 0.5 kg pair of running shoes would weigh 11.55 newtons on Jupiter, what is
the strength of gravity there? Fg = mg; 11.55 = .5g; 11.55/.5 = 23.1
b. If he same pair of shoes weighs 0.3 newtons on Pluto, what is the strength of
gravity on Pluto? Fg = mg; 0.3 = 0.5g; .3 / .5 = 0.6 = g
c. What does the pair of shoes weigh on earth? Fg = mg = 0.5 x 9.8 = 4.9
Do Section 3-2 in book on page 82. Answer ?s 1-8
140 / 2.12 = 66.0377 = m
Fg = mg = 66.0377 x 9.8 = 647.1695 N
195 lb --> kg
195 / 2.12 = 91.9811
Fg = mg = 91.9811 x 9.8 = 901.4148
Physical Science Page 2